1. Field of the Invention
This invention relates to a light-receiving member having sensitivity to electromagnetic waves such as light (herein used in a broad sense, including ultraviolet rays, visible light, infrared rays, X-rays, gamma-rays, and the like).
2. Description of the Prior Art
Photoconductive materials, which constitute photoconductive layers in solid state image pickup devices, image forming members for electrophotography in the field of image formation, or manuscript reading devices and the like, are required to have a high sensitivity, a high SN ratio [photocurrent (I.sub.p)/dark current (I.sub.d)], spectral characteristics matching to those of irradiating electromagnetic waves, a rapid response to light, a desired dark resistance value as well as no danger to human bodies during usage. Further, in a solid state image pick-up device, it is also required that the residual image should easily be treated within a predetermined time. Particularly, when an image forming member for electrophotography is assembled in an electrophotographic device as an office apparatus, said safety characteristic is very important.
Under these circumstances, amorphous silicon (hereinafter referred to as "a-Si") has recently attracted attention as a photoconductive material. For example, German OLS Nos. 2746967 and 2855718 disclose applications of a-Si to image forming members for electrophotography, and German OLS No. 2933411 discloses an application of a-Si to a photoelectric transducing reading device.
However, under the present situation, the photoconductive members of the prior art having photoconductive layers made of a-Si still require further improvement in a balance of overall characteristics including electrical, optical and photoconductive characteristics such as dark resistance value, photosensitivity and response to light, etc., and service environmental characteristics such as humidity resistance, and a longer stability.
For instance, when said photoconductive member is applied to an image forming member for electrophotography, residual potential frequently remains on it during the service time if a higher photosensitivity and a higher dark resistance are made at the same time. When such a photoconductive member is repeatedly used for a long time, various inconveniences often appear, such as accumulation of fatigue by repeated uses or so called ghost phenomenon wherein residual images are formed, or when the photoconductive member is used repeatedly at a high speed, the response is gradually lowered.
Further, a-Si has a relatively smaller coefficient of absorption of the longer wavelength light in the visible light region as compared with the shorter wavelength light. Accordingly, in the matching to the semiconductor laser now practically used, the longer wavelength light cannot effectively be utilized, when the ordinary halogen lamp or fluorescent lamp is used as the light source. Thus, there still remain various points to be improved.
On the other hand, when the irradiation light is not sufficient absorbed in the photoconductive layer, but when the amount of the light reaching the substrate is increased, interference due to multiple reflection may occur in the photoconductive layer to cause an "unfocused" image, in the case that the substrate itself has a high reflectance to the light transmitted through the photoconductive layer.
This effect will be increased, if the irradiated spot is made smaller to enhance resolution. Thus, this will be a great problem when a semiconductor laser is used as the light source.
Further, a-Si materials for the photoconductive layer may contain as the constituent atoms hydrogen atoms or halogen atoms such as fluorine atoms, chlorine atoms, etc. for improving their electrical, photoconductive characteristics; boron atoms, phosphorus atoms, etc. for controlling the electroconduction type as well as other atoms for improving other characteristics. The manner in which these constituent atoms exist therein may sometimes raise problems of electrical or photoconductive characteristics of the formed layer.
In many cases, for example, the life of the photocarriers generated by light irradiation in the formed photoconductive layer is not sufficiently long, or the charges injected from the substrate side cannot be sufficiently prevented at the dark portion.
Accordingly, together with an attempt to improve the characteristics of a-Si material itself, it is also required to overcome all the problems as mentioned above in designing of the photoconductive member at the same time.
The present invention is based results of extensive studies made comprehensively from the standpoints of applicability and utility of a-Si as a light-receiving member for image forming members for electrophotography, solid state image pick-up devices, reading devices, etc. It has now been found that the light-receiving member constituted of an amorphous material containing silicon atom (Si) as a matrix, especially, an amorphous material containing at least one of hydrogen atom (H) and halogen atom (X) in a matrix of silicon atom (Si), so-called hydrogenated amorphous silicon, halogenated amorphous silicon, or halogen-containing hydrogenated amorphous silicon [hereinafter referred to comprehensively as "a-Si(H,X)"] and an amorphous material containing silicon atom (Si) and germanium atom (Ge) as a matrix, especially, an amorphous material containing at least one of hydrogen atom (H) and halogen atom (X) in a matrix of silicon atom (Si) and germanium atom (Ge), so-called hydrogenated amorphous silicon germanium, halogenated amorphous silicon germanium, or halogen-containing hydrogenated amorphous silicon germanium [hereinafter referred to comprehensively as "a-SiGe(H,X)"], said light-receiving member being prepared with a design to have a specific structure as hereinafter described, not only exhibits practical very good characteristics but also surpasses the light-receiving members of the prior art in substantially all respects especially having markedly excellent characteristics as the light-receiving member for electrophotography and also excellent absorption spectrum characteristics on the longer wavelength side.